This application is based on and claims the benefit of priority of Japanese Patent Application No. 2001-349273 filed on Nov. 14, 2001, the disclosure of which is incorporated herein by reference.
The present invention relates to a motor having a brush holder between a yoke housing and a gear housing.
As a motor for a vehicular power window apparatus, a motor having a brush holder between a yoke housing and a gear housing is proposed. Because this kind of motor is generally installed in a door, it is easily soaked or covered with water.
During a motor operation, the temperature inside the motor rises. After the motor is turned off, the inside of the motor is cooled and the inside pressure of the motor begins to be negative pressure. At this time, if the motor is covered with water, the water is sucked into the motor through the connecting portions between the yoke housing, gear housing, and brush holder. Further, the water is likely to be stored in the motor. As a result, functional components in the motor, such as a bearing, are rusted, thereby causing defects to the motor operation.
Therefore, it is required to protect the motor from the water. For example, a breathing hole is formed on the yoke housing or the gear housing. With this, because pressure difference between the inside and outside of the motor is decreased through the breathing hole, entering of the water is suppressed even when the motor is covered with the water.
In this case, however, the breathing hole is closed with the water, depending on the position or opening direction of the breathing hole. As a result, the breathing hole does not operate properly and the water enters the motor form the breathing hole. Therefore, it is required to design the breathing hole without being covered with the water.
Because mounting positions of the motor are different depending on the types of vehicles, it is required to change the opening direction of the breathing hole in correspondence with the change of the mounting position of the motor. Also, preparing various yoke housings and gear housings in which breathing holes are formed in different directions causes disadvantages in costs and production.
Instead of changing the direction of the breathing hole in correspondence with the mounting position of the motor, it is proposed to cover the breathing hole with waterproof sheets to protect from the water. In this case, since it is not required to change the direction of the breathing hole, the direction of the breathing hole is standardized. However, since the waterproof sheet is required additionally, the number of parts is increased.
The present invention is made in view of the above disadvantages and an object of the present invention is to standardized parts of a motor and to decrease the number of the parts.
According to the present invention, a motor has a yoke housing rotatably enclosing an armature and a brush holder for holding brushes to slide-contact with the armature. The yoke housing is formed into a substantially cylindrical shape having a closed end at a side and an open end at an opposite side. The brush holder is fixed to the yoke housing to close the open end.
The brush holder is formed with a first opening being open toward the inside of the yoke housing, a second opening being open to the outside of the yoke housing, and a communication hole communicating between the first opening and the second opening inside the brush holder.
In the motor, when the pressure inside the yoke housing begins to be negative pressure after a motor operation, the outside air is sucked into the yoke housing from the second opening through the communication hole. Therefore, the negative pressure inside the yoke housing is cancelled.
According to the present invention, parts can be standardized and reduced. Also, manufacturing costs can be decreased and products efficiency is improved. Further, designing flexibility is improved.